BCB5: Categorizing TListView (vsReport)

I have another question which should emphasize my lack of intelligence.  I'm
writing a mail/newsreader (Outlook is getting on my nerves) and need to sort
messages into groups, as listed in a TTreeView component.  I'm already using
the TListItem data property for something else.  How can I specific which
group an item is in?  If necessary, could someone point me in the general
location of info regarding deriving a new component?  Also, (if the latter
is necessary) would I need to derive just TListItem, or TListView as well?

Thanks in advance,
~Josh K.
If the automobile had followed the same development cycle as the computer, a
Rolls-Royce today would cost $100, get a million miles to the gallon, and
explode once every few weeks, killing everyone inside.